1. Field of the Invention
The present invention relates to a wireless communication system and a wireless communication method for performing read/write communications between wireless IC chips provided to a plurality of articles piled up three-dimensionally on a dolly passing through a passage or a production line.
2. Description of Related Art
A wireless communication system, in which an electromagnetic wave from an antenna is radiated to RFID tags attached to a plurality of articles piled up three-dimensionally on a dolly passing through a passage or a production line so as to perform read/write communications between the RFID tags attached to the articles, has been developed.
In the wireless communication system, various methods are adopted to make an electromagnetic wave from an antenna arrive at RFID tags of a plurality of articles piled up three-dimensionally on a dolly. The methods will be described.
Japanese Patent Laid-Open Publication No. 2005-5876 discloses a configuration including an antenna for irradiating a recognition area with an inquiry electromagnetic wave and a reflecting plate arranged opposite thereto to thereby extend the recognition area. Japanese Patent Laid-Open Publication No. 2005-4532 discloses a configuration in which a plurality of antennas are arranged circumferentially around a turntable mounting a wireless data carrier. Japanese Patent Laid-Open Publication No. 2004-265112 discloses a configuration in which a plurality of antennas are arranged in a height direction around an article mounting part. Japanese Patent Laid-Open Publication No. 2005-192030 discloses a configuration in which an antenna is arranged in a space to be detected, and the space is scanned by the antenna.
It is true that the wireless communication systems disclosed in the above-mentioned patent documents are capable of effectively guiding the direct electromagnetic waves from the antennas or the electromagnetic waves reflected by the reflection plates to the RFID tags of the articles through utilizing the positional relation between the plurality of antennas and the reflection plates.
However, when using a plurality of antennas, or using reflecting plates, interference may be caused between electromagnetic waves directly arrived at the RFID tags from the antennas and electromagnetic waves reflected at the reflecting plates, depending on the directions of antenna faces of the RFID tags with respect to the radiating direction of the electromagnetic waves from the antennas, so there is a case where the both of the direct and reflected electromagnetic waves cannot be made incident on the RFID tags effectively. If such a phenomenon is caused, the RFID tags cannot decode data signals transmitted from antennas by electromagnetic waves, whereby read/write communications cannot be performed.